1. Field of the Invention
The present invention relates to a display.
2. Description of the Related Art
In an organic electroluminescent (EL) display, image quality deterioration such as luminance unevenness occurs if a drive current varies. Therefore, when an active matrix driving method is used in this display, the characteristics of a drive control element for controlling the magnitude of the drive current must be substantially the same between pixels. In this display, however, the drive control element is normally formed on an insulator such as a glass substrate, so the characteristics of the element easily vary.
U.S. Pat. No. 6,373,454 describes an organic EL display using a current mirror circuit in a pixel. This pixel includes an n-channel field-effect transistor (FET) as the drive control element, an organic EL element, a capacitor, an output control switch, a video signal supply control switch, and a diode-connecting switch.
The source of the drive control element is connected to a first power supply line at a low electric potential, and the capacitor is connected between the gate of the drive control element and the first power supply line. The output control switch is connected between the drain of the drive control element and the cathode of the organic EL element, and the anode of the organic EL element is connected to a second power supply line at a higher electric potential. The video signal supply control switch is connected between the drain of the drive control element and a video signal line, and the diode-connecting switch is connected between the drain and gate of the drive control element.
During a write period, the pixel including the current mirror circuit is supplied with a current signal Isig as a video signal. During a hold period following the write period, a drive current having a magnitude substantially equal to that of the electric current Isig flows between the drain and source of the drive control element. This makes it possible to eliminate the influence of not only a threshold value Vth but also the mobility, dimensions, and the like of the drive control element on the drive current.
In an active matrix display, some pixels are sometimes viewed as luminous dots or dark dots owing to disconnections or short circuits in the pixel circuit. Also, in an active matrix display, pixel columns or rows are sometimes viewed as luminous lines or dark lines owing to disconnections of scan signal lines or video signal lines.
When achieving the present invention, the present inventor has found that in an active matrix display in which a current signal is written as a video signal in a pixel circuit, a luminous dot with a luminous or dark line-like tail forms in an image in addition to the line- or dot-like luminance unevenness described above.